As the next-generation radio communication system for performing a higher speed communication as compared with the 3rd-generation and 3.5th-generation radio communication systems operated at present, LTE (Long Term Evolution) has been standardized in 3GPP (3rd Generation Partnership Project) which is the standardization body of a radio communication system.
The technical specifications of the LTE have been specified as 3GPP Release 8, and Release 9 which is an upgrade version of Release 8, and LTE Advanced which is a sophisticated version of the LTE, have been currently considered. In LTE Advanced, the adoption of relay transmission using a fixable or movable radio relay station called a relay node is planned (for example, see Non-Patent Document 1).
The radio relay station is a low-output relay base station connected to the radio base station (macro base station) via radio. The radio terminal connected to the radio relay station performs communication with the radio base station via the radio relay station. When the radio relay station is installed in transportation equipment such as a train or a bus and then the radio terminal present inside the transportation equipment is connected to the radio relay station, it is possible to perform communication under better conditions as compared to when a connection is established with the radio base station.
Furthermore, the radio terminal performs a handover in which the connection destinations are switched to a radio base station having a radio quality better than the currently-connected radio base station. The radio terminal can perform a handover not only between the radio base stations but also from the radio base station to the radio relay station. In such a case, the radio terminal performs a handover to a radio relay station having a radio quality better than the currently-connected radio base station.